1. Technical Field
The invention relates to a method of operating an automatic speed control system to assist a driver of a vehicle during an overtaking or passing process.
2. Background Art
Overtaking processes require the driver of a motor vehicle to coordinate a multiplicity of different tasks. These include, before the overtaking process starts, not only that the driver stays in the traffic lane but also that he maintains a minimum distance from the vehicle traveling ahead and observes any traffic on a further lane which is required for the overtaking process. In order to relieve the driver in maintaining a predefined velocity and following a vehicle traveling in front while maintaining a minimum distance therefrom, adaptive cruise control methods have been developed in which the acceleration and deceleration of the motor vehicle are adjusted on the basis of data detected by a sensor system (such as radar, lidar, or a vision system) in such a way that the velocity and/or distance from the vehicle traveling ahead are kept constant within a predefined range. Distance-related cruise control systems are known in which the control system adjusts to a predefined velocity if no preceding vehicle (traveling immediately ahead) is detected by the sensor system, and the control system is then adjusted to a predefined distance if such a vehicle has been detected in a corresponding distance range.
During an overtaking process it is necessary to intervene in such a control system because the adaptive cruise control system would otherwise not permit acceleration until the vehicle to be overtaken (the preceding vehicle) is located completely outside the traveling path of the overtaking vehicle or is no longer detected by the sensor system. Otherwise, the acceleration required for the overtaking process is usually already initiated by the driver before a lane change in order to be able to terminate the overtaking process within a relatively short time and in order to be able to more safely cut into the more quickly flowing traffic on the overtaking lane. In the interests of a harmonious and free-flowing overtaking process whose sequence corresponds to the driving style of a human driver, it is therefore desirable to adapt the automatic adaptive cruise control process as soon as the driver's intention to overtake can be detected.
DE 42 00 694 A1 discloses interrupting the adaptive cruise control process for a predefined time period if the driver indicates an intention to overtake by, for example, activating a turn indicator. This has the disadvantage that the automatic adaptive cruise control system which ensures that a safety distance from the preceding vehicle is maintained does not function during this time period.
As is described in EP 1 037 760 A1, before an overtaking process the setpoint value for the distance from the preceding vehicle, which is predefined for the adaptive cruise control process, can be reduced to a minimum permissible distance. If the system detects a risk of collision, the overtaking process is aborted and the vehicle brakes may be applied, if appropriate.
U.S. Pat. No. 6,842,687 B1 discloses a method for assisting the driver of a motor vehicle during an overtaking process in which the distance from a preceding vehicle on the same lane and the distance from a vehicle traveling directly ahead on the overtaking lane are measured. If a desire to overtake on the part of the driver is detected, an overtaking speed is calculated and an adjustment to the overtaking speed is superimposed on the steady-state adaptive cruise control system. In the above-mentioned methods, an acceleration which corresponds to the adaptive cruise control and/or cruise control process is used; however, this is generally set to a rather low value for reasons of travel comfort and economy. As a result, it is not possible to carry out the overtaking process in an optimal way. Also, such a sequence differs from the driving style of a human driver in so far as said driver would be likely to use a significantly increased acceleration for overtaking.